1. Field of the Invention
The invention in general relates to crystal growth and more particularly to the production of silicon carbide crystals with improved processability and defect and impurity reduction.
2. Description of Related Art
Silicon carbide is being used extensively as a semiconductor material for various electronic applications. Semiconductor devices of silicon carbide have the ability to operate at higher voltages and temperatures than conventional silicon or gallium arsenide devices thus providing for higher power devices with reduced cooling requirements. Electronic applications for silicon carbide semiconductor devices include compact, low cost airborne, ship and ground radars, aircraft engine and flight controls, electric tank and ship propulsion systems and satellite communications, to name a few. In the commercial sector, silicon carbide may be used in the field of high definition television, industrial power conditioning, nuclear control and instrumentation and electric vehicle power trains.
Pure silicon carbide crystals may be grown in a variety of ways, one of which utilizes a seed crystal of silicon carbide positioned within a furnace which also includes a source of pure silicon carbide. The source is heated to a temperature whereby the silicon carbide sublimates and is deposited upon the seed crystal. In one process, the seed crystal is positioned within a container having a growth cavity for the crystal. The container is of a material, such as graphite, which can withstand the temperatures experienced within the furnace.
As silicon carbide is deposited from the source, a silicon carbide crystal, called a boule, is grown within the container and comes into contact with the wall of the growth cavity and may actually fuse with it. After the boule is grown to the desired size, the container is removed from the furnace for separation of the grown crystal. During the separation process the container is physically ground away. Due to the interaction of the crystal periphery with the container, when the boule surface is reached the grinding process must continue at a much slower rate to avoid undue stressing of the crystal. The total grinding operation is a laborious and extremely time consuming process and reduces the total area of the final substrates derived from the boule.
In addition, the interaction of the boule with the wall of the growth container may cause or contribute to (a) undesired formation of secondary silicon carbide grains nucleated on the container wall, as well as (b) low angle boundaries which are misorientations of local areas of the substrate.
The present invention obviates the tedious grinding of the boule surface, improves crystal purity, and reduces or eliminates various defects.